Magnesium base alloy containing small amounts of rare earth metal



' Alloying constituent:

United States Patent 0 "ice 3,157,496 lvIAGNESIUlvi EAE ALLOY CGNTG SMALL AMGUNTS till RARE EARTH METAL George S. Foerster, R/iidland, Mich, assignor to The Dow (Ihemical Qompany, Midland, Mich, a corporation of Delaware No Drawing. (Zontinuah'on of application Ser. No. 73,318, Dec. 27, 1960. This application gept. 13, 1962, Ser. No. 223,526

11 Gaims. (Cl. 75168) This invention relates to a magnesium-base alloy containing at least 85 weight percent of magnesium and is more particularly concerned with a thorium-free magnesium alloy having primarily the following composition:

Weight percent, balance Mg Rare earth metal 0.05 to 2 Zinc 0.05 to 0.5

The alloy of the invention exhibits excellent high temperature properties comparable to the thorium-containing alloys but avoids the use of expensive thorium metal. both at ambient room temperature and at elevated tem peratures such as 400 F.

The rare earth metals suitable for use in preparing the present alloy are: cerium, lanthanum, praseodymium, neodymium, didymium (a mixture of rare earth metals having praseodymium and neodymium as major constitucuts) or misch metal (a mixture or" rare earth metals). Any of the foregoing rare earth metals may be used alone or in any combination in compounding the alloy. A commercially available misch metal, sometimes called cerium misch metal, containing from 35 to 80 percent of cerium, the balance being rare earth metals and up to 5 percent of non-rare earth metal, is the preferred rare earm metal ingredient of the alloy because of availability, although the use of didymium permits the obtaining of somewhat higher strength properties at given rare earth metal concentrations.

The alloy may be further improved by the addition of from 0.2 to 2 percent by Weight of manganese as a matrix strengthen ng component. if desired, a small amount of zirconium, e.g., not more than about 0.2 percent, may

be beneficially employed concurrently with manganese for its grain refining action, although when substantially larger amounts of zirconium are added, there is a tendency for zirconium and manganese to precipitae from the alloy together.

if desired, small amounts of one or more other matrix strengthening components which are well known in the magnesium art may be added to the alloy provided they are compatible therewith, i.e., do not precipitate componets therefrom during alloy preparation or otherwise adversely effect high temperature properties of the alloy. However, it is preferred that the alloy of the invention contain at least 95 percent by weight of magnesium.

The alloy also exhibits good resistance to creep 3,1514% Patented Nov. 17, 1964 The composition is further limited to alloys in which the proportion of zinc is in the range of from 1 to /3 part of zinc per part of rare earth metal in compositions containing up to about 0.6 percent of rare earth metal, and the proportion of zinc is in the range of from 0.2 to 0.5 percent by weight in compositions containing from about 0.6 to 2 percent of rare earth metal.

While higher physical strength properties are generally obtainable at higher cost upon employing higher proportions of rare earth metal, it is usually to be desired for economic reasons that smaller proportions of rare earth metal be used. Thus, a desirable range of proportions of the present alloy is at least 95 percent of magnesium, from 0.2 to 1 percent of rare earth metal and from 0.067 to 0.5 percent of zinc. I

The most preferred proportions of the alloying components in the present alloy are, by weight, from 0.2 to 0.5 percent of rare earth metal and from 0.067 to 0.5 percent of zinc. The most preferred weight ratio of rare earth metal to zinc is about 2 parts of rare earth metal per parL of zinc. The most preferred proportion of matrix strengthening component is by Weight from 0.5 to 1 percent of manganese.

The alloy may be made in the desired proportions according to the invention by melting together the alloying ingredients in proper porportions or by using hardeners of magnesium alloys containing the alloy constituents.

Protection iromvoxidation during alloying is effected by the use of a magnesium chloride-free saline flux as in conventional alloying. The molten alloy may be flux refined by stirring the alloy with additional flux. The soreiined alloy is allowed to settle and then is separated from the flux as by decanting into a suitable casting mold, e.g., a slab mold for rolling stock.

EXAMPLES To illustrate the advantageous results which can be achieved by the present invention, a series of compositions according to the invention were prepared and cast into respective rolling slabs (e.g., 2 inches x 4 inches x 8 inches). Each slab was treated as follows: The faces of the slab were scalped to remove surface impurities or inclusions. The slab was heated to about 900 F. and rolled into sheet form. Test coupons were cut from the so-prepared sheet and subjected to physical testing. Compressive yield strength and tensile strength tests were carried out in the longitudinal direction of rolling. The alloy compositions, test conditions and the static strength properties are listed in Table 1.

By way of comparison, magnesium-rare earth metal alloys containing, respectively, no zinc, and zinc in rare earth metal to zinc ratios outside the scope of the present invention were prepared and rolled into sheet form and similarly tested. The results of these comparision tests are listed in Table I.

By examination of the data in Table I, it may be seen that the alloy of the invention exhibits better high temperature strength properties and greatly increased creep resistance at elevated temperatures.

Table I Composition Per- Physical Properties cent by Weight Creep Resistance at 5,000 Test N 0. Sheet Preparap.s.i. for 100 hrs., Percent Temp, 15

tion (Temper) 2 At 75 F. At 300 F. Creep MM Zn %E TYS CYS TS TYS 1 Balance magnesium;

2 H24 Rolling slab reduced 92% by hot rolling at 850 F., then reduced 30% in one pass at 750 F., (450 F. exit), and heat treated 1 hour at 500 F.

eta 7 -O=Same as H24 except terminal heat treatment is at 700 F. instead of 500 F.

%E =Percent elongation.

TYS=Tensi1e yield strength in 1.000s of p.s.i.

CYS= Compression yield strength in 1,000s of p.s.i. TSf= Ultimate tensile strength in 1,000s of p.s.i.

H 26=Rolling slab reduced 94% by hot rolling at 800 F., then reduced in one pass at 450 F. (320 F. exit), and heat treated 1 hour at 275 F.

Ran away=Creep extension v. time curve became very steep so that the extension could not be measured.

Tab le 11 See footnotes, bottom of Table 1.

'Additional compositions according to the invention, containing manganese in addition to zinc and rare earth metal, were prepared and cast'into rolling slabs. Each rolling slab was reduced 92 percent (in thickness) by hot rolling at 850 F., then reduced 30 percent in one pass at 750 F. (450 F. exit), and heat treated 1 hour at 700 F. Test coupons cut from the so-prepared sheet were tested for resistance to creep at 400 F. In Table II are listed the compositions tested and the percent extension in 100 hours.

Still an additional composition according to the invention containing, by Weight, from 0.4percent of manganese and 0.09 percent of zirconium in addition to 1.3 percent of didymium and 0.3 percent of .zinc and the balance commercial magnesium, wasprepared and cast into rolling. slabs each 2 inches X4 inches x 8 inches. Each slab wasscalpedto removesurface impurities or inclusions, heated to about 900 F. and reduced in thickness to about 0.1 inch sheet by rolling. During the rolling operation, the partially reduced. slab was occasionally reheated to prevent it cracking on being rolled. The sheet was heat treated. at about 1000 F. for'an hour, quenchedpand cold rolled 1-2 percent per pass through steam heated rolls'for a total reduction in the range of 15 to 50 percent. The cold rolled sheet was then heat treated at about 500 F. for an hour. Test coupons were out from the so-prepared sheet and subjected to physical testing in the longitudinal direction of rolling. The results of tests conducted at both 75 F. and 600 F. are listed in Table 111.

Table III Physical Properties of Sheet, $trengths in 1,000s of p.s.i.

Test Cold Rolled 15% and Heat Cold Rolled 50% and Heat Temp. Treated 1 Hour at 500 F. Treated 1 Hour at 500 F.

%E'- TYS CYS TS %E' 'IYS CYS TS 40 75 F 4 37 27 42 2 39 3s 4s 600 F 45 11 18 68 5 12 Among the advantages of the alloy of the invention a is good weldability Without stress relief.

This application is a continuation of my copending application, Serial No. 78,318, filed December 27, 1960.

I claim: 7 1. The improvement in thorium-freemagnesimn base alloys consisting essentially of a rare earth metal content in the range of 0.05 to 2 percent by weight and a zinc content in the range of 0.05 to 0.5 percent by weight, and the balance magnesium which consists in:

maintaining the proportion of zinc in the range from 1 to' /s part of zinc'per part'ofrare earth metal in compositions containing up to about 0.6"percent by Weight of rare earth metal and the proportion of zinc being in therange of from 0.2 to 0.5 percent by weight in compositions ccntainingfrom about 0.6

to 2 percent by weight of rare earth metal. 2. Theimprovement in thorium-free magnesium base alloys consisting essentiallyof from 0.05 to 2 percent by weight of rare earth metal, from 0.05'to 05 percent by weightof zinc, from 0.2 to 2 percent 'by weight of man of zinc, and having a rare earth metal content in the range of 0.2 to 1 percent by weight, and the balance magnesium which consists in:

maintaining the proportion of zinc at about 1 part of zinc per 2 parts of rare earth metal.

4. The improvement in thorium-free magnesium base alloys consisting essentially of from 0.2 to 1 percent by weight of rare earth metal, from 0.067 to 0.5 percent by weight of zinc, from 0.5 to 1 percent by weight of manganese, not more than 0.2 percent by weight of zirconium, and the balance magnesium which consists in:

maintaining the proportion of zinc in the range of from 1 to /3 part of zinc per part of rare earth metal in compositions containing up to about 0.6 percent by Weight of rare earth metal, and the proportion of zinc being in the range of from 0.2 to 0.5 percent by Weight in compositions containing from about 0.6 to 1 percent by weight of rare earth metal.

5. The improvement in thorium-free magnesium base alloys consisting essentially of rare earth metal in the range of 0.2 to 0.5 percent by weight, a zinc content in the range of 0.057 to 0.5 percent by Weight, and the bflance magnesium which consists in:

maintaining the proportion of zinc in the range of from 1 to /3 part of zinc per part of rare earth metal.

6. The improvement in thorium-free magnesium base alloys consisting essentially of up to about 0.25 percent by weight of zinc, and having a rare earth metal content in the range of 0.2 to 0.5 percent by weight, and the balance magnesium which consists in:

maintaining the proportion of zinc at about 1 part of zinc per 2 parts of rare earth metal.

7. The improvement in thorium-free magnesium base alloys consisting essentially of from 0.2 to 0.5 percent by weight of rare earth metal, from 0.067 to 0.5 percent by Weight of zinc, from 0.5 to 1 percent of manganese,

not more than 0.2 percent by weight of zirconium, and the balance magnesium which consists in;

maintaining the proportion of zinc in the range of about 1 to 1 3 part of zinc per part of rare earth metal.

8. A magnesium base alloy'consisting essentially of: from 0.2 to 0.5 percent by weight of rare earth metal, zinc in the proportion of about 1 part of zinc per 2 parts of the rare earth metal and the balance magnesium.

9. A ma nesium base alloy consisting essentially of: from 0.2 to 0.5 percent by weight of rare earth metal, zinc in the proportion of about 1 part per 2 parts of the rare earth metal, about 0.5 percent by weight of manganese, not more than 0.2 percent by weight of zirconium and the balance magnesium.

10. A magnesium base alloy consisting essentially of: from 0.2 to 0.8 percent by weight of rare earth metal, from 0.1 to 0.4 percent by Weight of zinc, and the balance magnesium, the proportion of zinc being in the range of 1 to /E; part of zinc per part of rare earth metal.

11. A magnesium base alloy consisting essentially of: from 0.2 to 0.8 percent by weight of rare earth metal, from 0.1 to 0.4 percent by weight of zinc, from 0.5 to 0.1 percent by weight of manganese, up to 0.2 percent by weight of zirconium, and the balance magnesium, the proportion of zinc being in the range of 1 to /3 part of zinc per part of rare earth metal.

References Cited in the file of this patent UNITED STATES PATENTS 115,813 Australia Sept. 

1. THE IMPROVEMENT IN THORIUM-FREE MAGNESIUM BASE ALLOYS CONSISTING ESSENTIALLY OF A RARE EARTH METAL CONTENT IN THE RANGE OF 0.05 TO 2 PERCENT BY WEIGHT AND A ZINC CONTENT IN THE RANGE OF 0.05 TO 0.5 PERCENT BY WEIGHT, AND THE BALANCE MAGNESIUM WHICH CONSISTS IN: MAINTAINING THE PROPORTION OF ZINC IN THE RANGE FROM 1 TO 1/3 PART OF ZINC PER PART OF RARE EARTH METAL IN COMPOSITIONS CONTAINING UP TO ABOUT 0.6 PERCENT BY WEIGHT OF RARE EARTH METAL AND THE PROPORTION OF ZINC BEING IN THE RANGE OF FROM 0.2 TO 0.5 PERCENT BY WEIGHT IN COMPOSITIONS CONTAINING FROM ABOUT 0.6 TO 2 PERCENT BY WEIGHT OF RARE EARTH METAL. 